Various devices and systems such as computing devices, mobile communication devices, automotive equipment, industrial equipment, home white goods, and entry systems may require an authentication method to protect against unauthorized access. Fingerprint authentication using fingerprint sensors may protect an apparatus or system against unauthorized access.
Fingerprint sensors may use various capacitive sensing methods to image a fingerprint pattern, where imaging a fingerprint means detecting a fingerprint and generating a set of data values, or “fingerprint data,” that represents the fingerprint in digital format. The fingerprint data may be an image or other information specific to a fingerprint. This method requires direct contact or close proximity of the portion of the finger comprising the fingerprint, or “finger pad,” with the sensor surface. A very thin cover, or overlay, may be disposed over the sensor surface. Thick overlays between the fingerprint and the fingerprint sensor may obscure fingerprint features.
There may be a variety of situations when a user may want to image a fingerprint through a thick material. A user may want to image a fingerprint using a sensor which is overlayed by a thick material to protect the sensor (or the device which includes the sensor) against harmful environmental factors, such as cold and water, and harmful physical factors, such as sharp objects and corrosive chemicals, or to improve the appearance of the fingerprint sensor, such as by providing a continuous surface with a touchscreen. A protective enclosure or cover may be fabricated with rigid material, such as, but not limited to, glass or plastic, or flexible material, such as, but not limited to, fabric or film. A protective enclosure may completely enclose a device or may partially enclose a device. Current fingerprint sensors cannot image fingerprints through thick material. Using an enclosure or cover material that is thin enough to enable fingerprint sensing may limit the protective effectiveness of the enclosure or film. If using a thick enclosure or cover material, the user may have to remove the device from the enclosure or cover to enable fingerprint sensing. Removing the cover or enclosure may be inconvenient for the user and and/or may risk damaging the device. It is desirable to create a material which can overlay the sensor where the material that is thick enough for protection but enables accurately imaging a fingerprint through the material.